In theory, the conductor diameter must comply with the declared parameters. For example, if it is indicated on the marking that the cable is 3 x 2.5, then the conductor cross section should be 2,5 mm2. In fact, it turns out that the different size can differ by 20-30%, and sometimes more. What threatens it? Overheating or placing isolation with all the ensuing consequences. Therefore, before buying, it is desirable to find out the size of the wire to determine its cross section. How exactly consider the cross section of the wire in diameter and will find out further.
How and how to measure the diameter of the wire (wire)
To measure the diameter of the wire, the caliper or micrometer of any type (mechanical or electronic) is suitable. It is easier to work with electronic, but they are not all. It is necessary to measure the living well without isolation, therefore it is pre-moved it or remove the small piece. This can be done if the seller is allowed. If not, buy a small piece for testing and spend the measurements on it. On the insulation, the conductor measure the diameter, after which it is possible to determine the actual cross-section of the wire on the sizes.
Measurements of the diameter of the wire micrometer are more accurate than a mechanical caliper
What is the measuring device in this case better? If we talk about mechanical models, then micrometer. It has accuracy of measurements above. If we talk about electronic options, then for our purposes they both give quite reliable results.
If there is neither a caliper, nor micrometer, capture a screwdriver and a ruler. We have to clean a pretty decent piece of the conductor, so without buying a test pattern this time is hardly hampered. So, remove isolation from a piece of wires 5-10 cm. Wash the wire on the cylindrical part of the screwdriver. The coils are placed close one to another, without clearance. All turns must be complete, that is, the "tails" of the wires must be stitching in one direction - up or down, for example.
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Determining the wire diameter using a ruler
The number of turns is not important - about 10. It is possible more or less, just to divide it easier. Throwing turns, then apply the resulting winding to the ruler, aligning the beginning of the first turn with a zero mark (as in the photo). Measure the length of the area occupied by the wire, then it divides it to the number of turns. Get the wire diameter. That's it simple.
For example, we consider what the size of the wire shown in the photo above. The number of turns in this case is 11, they occupy 7.5 mm. We divide 7.5 to 11, we get 0.68 mm. This will be the diameter of this wire. Next, you can search for the section of this conductor.
We are looking for a wire section in diameter: formula
Wires in the cable have a circle in cross section. Therefore, in the calculations, we use the formula of the area of the circle. It can be found using radius (half of the measured diameter) or diameter (see formula).
Determine the cross section of the wire in diameter: formula
For example, we calculate the cross-sectional area of the conductor (wire) in size calculated earlier: 0.68 mm. Let's first use the formula with a radius. First we find a radius: we divide the diameter for two. 0.68 mm / 2 = 0.34 mm. Next this figure we substitute in the formula
S = π * R2 = 3,14 * 0.342 = 0.36 mm2
It is necessary to count this way: first we will be erected into a square 0.34, then multiply the value obtained by 3.14. Received a cross section of this wire 0.36 square millimeters. This is a very thin wire, which is not used in power networks.
Let's calculate the cable cross section in diameter using the second part of the formula. It should be exactly the same meaning. The difference can be in thousands of shares due to different rounding.
S = π / 4 * d2 = 3.14 / 4 * 0,682 = 0.785 * 0,4624 = 0.36 mm2
In this case, we divide the number 3.14 to four, then we will be erected into a square, the two figures obtained with a variant. We get a similar value, as it should be. Now you know how to find out the cable cross section in diameter. Which of these formulas are more convenient for you, that and use. No difference.
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Table matching the diameters of the wires and their cross-section area
Conduct settlements in the store or in the market does not always want or have the opportunity. In order not to spend time on calculations or not mistaken, you can use the table of conformity of diameters and sections of the wires in which there are the most common (regulatory) dimensions. It can be rewritten, print and capture with you.
| Conductor diameter | Conductor section |
|---|---|
| 0.8 mm | 0.5 mm2 |
| 0.98 mm | 0.75 mm2 |
| 1,13 mm | 1 mm2. |
| 1.38 mm | 1.5 mm2 |
| 1.6 mm | 2.0 mm2. |
| 1.78 mm | 2.5 mm2 |
| 2.26 mm | 4.0 mm2. |
| 2.76 mm | 6.0 mm2 |
| 3.57 mm | 10.0 mm2 |
| 4.51 mm | 16.0 mm2. |
| 5.64 mm | 25.0 mm2. |
How to work with this table? As a rule, on cables there is a marking or tag on which its parameters are indicated. There is a cable marking, the amount of lived and their cross section. For example, running 2x4. We are interested in the parameters of the veins. And these are numbers that stand after the sign "x". In this case, it is stated that there are two conductor having a cross-section of 4 mm2. So we will check whether this information is true.
To check, measure the diameter of any of the described methods, then refer to the table. It indicates that with such a section in four square millimeters, the size of the wire must be 2.26 mm. If you have the same or very close measurements (measurement error exists, as non-ideal instruments), everything is fine, you can buy this cable.
The stated dimensions are far from always correspond to the real.
But much more often the actual diameter of the conductors is significantly less than the stated. Then you have two ways: search for a wire of another manufacturer or take a larger cross section. For him, of course, you will have to overpay, but the first option will require a rather large period of time, and not the fact that you will be able to find the corresponding GOST cable.
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The second option will require more money, since the price significantly depends on the declared section. Although, not a fact - a good cable made in all standards may be even more expensive. This is understandable - copper costs, and, often, and isolation, while compliance with technology and standards, is much larger. Therefore, manufacturers and chitryat, reducing the diameter of the wires - to reduce the price. But such savings can turn into trouble. So be sure to measure before purchasing. Even proven suppliers.
And also: inspect and swell insulation. It should be thick, solid, have the same thickness. If, in addition to changing the diameter, the problem is also with isolation - look for a cable of another manufacturer. In general, it is advisable to find products that meets the requirements of the GOST, and not done on that. In this case, there is hope that the cable or the wire will serve for a long time and without problems. Today it is not easy to do, but if you divor the wiring in the house or connect electricity from the post, the quality is very important. Therefore, it is probably to search.
How to determine the cross section of the stranded wire
Sometimes conductors are used stranded - consisting of many identical thin wires. How to calculate the cross section of the wire in diameter in this case? Yes, just too. Perform measurements / calculations for one wire, consider their number in the beam, then multiply on this number. Here you will learn the cross-sectional area of the stranded wire.
The cross section of the stranded wire is considered similar